Ringworm is an unsightly skin lesion, usually circular and hairless, caused by a fungus infecting the hair and outer layer of skin. Trichophyton verrucosum is the principal agent affecting cattle with other fungi less commonly involved. Ringworm is a zoonosis. Human infection is usually on exposed skin such as arms and neck, and is noticed when circular, itchy, red and exudative lesions appear after close contact with cattle.
Ringworm is rare in production sheep and goats. It can be a problem in young show sheep that have their skin and fleeces scrubbed clean. It is presumed this reduces effectiveness of local protective barriers allowing fungi to invade. It is unlikely to occur in production sheep and goats in the live export process.
Tough, easily dispersed spores provide a source of environmental contamination. Transmission is via animals contacting infective spores in the environment or by close contact between animals.
Bos indicus breeds are less affected than Bos taurus breeds. Conditions in the live export process are ideal for spread due to the combination of susceptible cattle, high humidity, reduced direct sunlight, and deck washing to wet the skin.
The presence of ringworm lesions can influence export market access and value. Affected animals may be rejected or have their market value downgraded if lesions are detected at destination.
Lesions are typically circular, up to 3 cm diameter with larger patches the result of coalesced lesions. The head and neck are usually most affected but lesions may occur on other prts of the body. Initially, the skin is moist and reddened; later it is dry, scaly and grey.
Laboratory confirmation requires deep skin scrapings or biopsy of lesions for microscopic demonstration or isolation of the organism.
Differential diagnoses include warts, bovine herpes mammilitis virus, dermatophilosis and stephanofilariasis. Lumpy skin disease which is exotic to Australia should also be considered.
Ringworm heals with or without treatment in about 8 weeks. Treatments may not shorten the time to complete healing of lesions. Not treating animals and letting the disease run its course is a common response to ringworm.
Treatment with imidazole spray may stop progression of lesions and slow the spread to other animals. Chlorine and iodine based compounds are much less effective.
Cationic alkyl dimethylbenzyl ammonium halides, appropriately diluted, may be blanket sprayed on affected cattle in pens at sea to minimise spread of spores.
Highly effective cattle ringworm vaccines used for treatment and prevention are available overseas but not in Australia.